This invention relates to stacking apparatus for asbestos sheets.
In the manufacture of flat or corrugated asbestos cement sheets, it is known to stack the sheets immediately after moulding them, and therefore while they are still fresh, on trolleys and to interleave the sheets with plate-like patterns, generally consisting of flat or corrugated metal sheets, which are delivered to the stacking station by means of other trolleys. In this manner, mixed stacks of a determined number of sheets interleaved with patterns are formed.
The present invention is concerned with apparatus for stacking asbestos cement sheets interleaved with patterns of the kind comprising feeding means for feeding fresh asbestos cement sheets, first and second flanking guideways for guiding respectively pattern-carrying trolleys and trolleys carrying mixed stacks of sheets interleaved with patterns, a bridge structure arranged above said guideways and said feeding means, a carriage displaceably mounted on the said bridge structure and provided with respective suction boxes for picking-up, transporting, and depositing the said sheets and the patterns, a trolley elevator in the area of formation of the stack of interleaved sheets and patterns, and a transfer device for transferring the said trolleys from one to the other of the said guideways, outside the bridge structure.
It is known in the context of mass production of asbestos sheets to provide elevators with automatic controls to keep constant both the upper level of the mixed stack of sheets and patterns and the upper level of the patterns alone, so as to limit the vertical travel of the suction boxes which pick up the sheets and patterns thus speeding-up the working cycle of the stacking apparatus.
In known apparatus of the kind described above, when a trolley for carrying a pattern is empty, the following operations are effected:
I. lowering of the elevator to a level where the empty pattern-carrying trolley is placed on the respective guideway;
Ii. moving a trolley loaded with patterns to a location under the respective pick-up suction box, and further removal of the empty trolley from the operational area of the said suction box, and
Iii. raising the elevator so as to bring the upper level of the stack of pattern plates on the trolley, to the level predetermined relatively to the pick-up suction box.
These three operations must be effected in an interval of time shorter than that required by the associated sheet manufacturing machine to produce a single sheet, since it would otherwise be necessary to lose one or more sheets by consigning them to a kneading machine to recover the material of the sheets.
Similarly, when the formation of a stack of sheets and patterns is completed on a trolley, that is to say, when the last of a predetermined number of sheets has been placed on the top of the stack, it is necessary to carry out the following operations:
i. moving of a pattern picked-up from the pattern-carrying trolley, and placing it on the top of the stack of sheets and patterns, since it is known that the stack must be topped by a pattern;
ii. lowering of the elevator to bring the mixed stack on the trolley onto the respective guideway;
iii. moving of a trolley, which is empty, except for one pattern, under a pick-up suction box, for positioning of the sheets and subsequent removal of the trolley loaded with sheets and patterns, and
iv. raising of the elevator, to bring the upper level of the empty trolley to the level predetermined with respect to the relevant suction box.
These four operations must be effected in a shorter period of time than that required by the machine to produce one sheet, otherwise wastage occurs. In practice, the time available to effect the last three operations is little more than half the time taken to produce one sheet, which in effect, is a very short time for carrying out these operations satisfactorily.
The above two series of operations related to the pattern carrying trolley and the mixed-stack trolley generally take place at different times, and therefore, the loss of even a single sheet at every trolley changing operation, entails a loss of at least two sheets for every cycle of loading a trolley with sheets and patterns.
Apart from the loss of productivity with such known apparatus, there is the further disadvantage caused by the introduction into the asbestos cement mixture of a considerable amount of reclaimed material coming from the waste sheets, which adversely alters the mixture, and increases the difficulty of operating a continuous, automatic machine for the production of sheets, with consequent loss of product quality.
Since in the operations relating to the changing of the pattern carrying trolleys, more time is available than in the case of the mixed stack carrying trolleys, it may be thought possible to shorten the changing time of the trolleys by increasing their speed of travel. However, this solution is not possible in practice, because the introduction of significant accelerations would cause the patterns, which are lubricated over their entire areas, to slide one upon the other, and damage their extremities by knocking against the aligning stops of the pattern stack. Similar trouble would also be experienced with the trolleys carrying the mixed sheets and patterns, the height of which sometimes exceeds one meter.
In consequence, even with the most advanced conventional equipment, with a high rate of production of asbestos sheets, it is not possible to effect a change of trolleys without the loss of at least one sheet.
The object of this invention is to eliminate the loss of sheets when changing trolleys, while maintaining a high rate of production of fresh sheets.